Automatic test systems for testing printed circuit boards utilize a multitude of points on the printed circuit board to which are applied various stimulus signals. Simultaneously with the application of these stimulus signals, other points on the printed circuit board are monitored for a response to the stimulus signals. By analyzing the results of the responses, it can be determined which points on the printed circuit board are connected to each other and which points are isolated. By comparing this data to the data of a reference, known good printed circuit board, or design data used to create the printed circuit board, it can be determined if the board was properly manufactured.
Typical printed circuit board test systems, such as shown in U.S. Pat. No. 4,833,402 include large numbers of programmable signal drivers for producing the various stimulation signals to be applied to the printed circuit board under test. These systems further include a large number of programmable signal receivers for receiving the signals produced by the printed circuit board under test in response to the stimulus signals. Due to rapid advances in surface mount technology and multi-layer fabrication techniques, many of the circuit boards require large numbers of test points or points located on the circuit board with minimal spacing such that these printed circuit boards exceed the capabilities of present automatic test systems.
Due to the high cost of electronic test circuity to improve the capability of existing test systems to handle present day circuit boards, it is clear that a need exists for printed circuit board test systems to reduce the number of test points required to test a circuit board while still ensuring that a complete and accurate test of a printed circuit board is achieved.